This invention relates to superconductor cables and more particularly to a superconductor cable made from a torsionally twisted multi-layer tape conductor stack.
A significant amount of worldwide effort has been devoted over the last decade to development of High Temperature Superconductor (HTS) wires of BSCCO-2223, BSCCO-2212 and YBCO for various electronic device applications such as transformers, fault current limiters, energy storage, magnets and power transmission cables. These practical applications demand high current capacities of the HTS superconductors without accompanying AC losses or magnetic flux coupling losses.
Current capacity of superconducting conductors can be increased with a parallel arrangement of the wires. However, flux couplings created in the loop circuits among the superconducting wires generate significant heat of resistive and magnetic hysteresis losses in the superconducting wires. The magnetic flux coupling between superconducting wires has been easily reduced by a transposition technique of twisting wires about each other if the wires are circular types such as NbTi and Nb3Sn superconductors. However, the twisting transposition technology has not been used for HTS superconducting tapes of thin flat shapes (typically 0.1 mm thick and 4 mm wide).
On the other hand, a round wire of BSCCO-2212 HTS superconductor has been developed, and high current cables using a conventional Rutherford type cabling method have been manufactured. [T. Hasegawa, J. Nishioka, N. Ohtani, Y. Hikichi, R. Scanlan, R. Gupta, N. Hirano, and S. Nagata, “12 kA HTS Rutherford cable,” IEEE Transactions on Applied Superconductivity, vol. 14, No. 2, pp. 1066-1069, 2004.]
Another successful development of a high current cable for flat tape HTS superconductors is the Continuously Transposed Cable (CTC) technology. This cabling method for a flat HTS tape has been developed based on a roebl cabling. The cabling concept of the roebling is seen, for example, in U.S. Pat. No. 2,249,509 of Welch, et al., and also recent U.S. Pat. No. 5,331,800 of W. Schaumburg, H. Gottschling, “Apparatus for making a cable by roebling rectangular cross-sectioned strands”. The CTC technology has been developed by General Cable Superconductors Ltd. [R. A. Badcock, N. J. Long, M. Mulholland, S. Hellmann, A. Wright, and K. A. Hamilton, “Progress in the Manufacture of Long Length HTS Roebel Cables,” in proceedings of ASC 2008, and N J Long, R Badcock, P Beck, M Mulholland, N Ross, M Staines, H Sun, J Hamilton, R G Buckley, “Narrow strand YBCO Roebel cable for lowered AC loss,” Journal of Physics: Conference Series 97 (2008) 012280].
The CTC method requires cutting a flat HTS tape in a specially designed zigzag pattern instead of bending used for the roebling, and assembling the flat tapes to form a transposed cable. The CTC technology has a difficulty developing a large conductor due to the fabrication method of the roebling. So far the CTC cable current of 2 kA using 17 tapes of 5 mm width has been fabricated.
The applications of high current HTS superconductors is growing in the area of electric transmission of AC and DC power. [D. Politano, M. Sjostrom, G. Schnyder and J. Rhyner, “Technical and economical assessment of HTS cables,” IEEE Transactions on Applied Superconductivity, vol. 11, No. 1, pp. 2477-2480, 2001. P. Chowdhuri, C. Pallem, J. A. Demko and M. J. Gouge, “Feasibility of electric power transmission by DC superconducting cables,” IEEE Transactions on Applied Superconductivity, vol. 15, No. 4, pp. 3917-3926, 2005. M. Hirose, T. Masuda, K. Sato and R. Hata, “High-temperature superconducting (HTS) DC cable,” SEI Technical review, 61, January 2006. J. F. Maguire, F. Schmidt, S. Bratt, T. E. Welsh, J. Yuan, A. Allais and F. Hamber, “Development and demonstration of a HTS Power cable to operate in the Long Island power authority transmission grid,” IEEE Transactions on Applied Superconductivity, vol. 17, No. 2, pp. 2034-2037, 2007. C. S. Weber, R. Lee, S. Ringo, T. Masuda, H. Yumura and J. Moscovic, “Testing and demonstration results of the 350 m long HTS cable system installed in Albany,” IEEE Transactions on Applied Superconductivity, vol. 17, No. 2, pp. 2038-2042, 2007.] Recently, some resources have been applied to DC power cable development, primarily in Japan. [S. Yamaguch, M. Hamabe, I. Yamamoto, T. Famakinwa, A. Sasaki, A. Iiyashi, J. Schltz and J. Minervini, “Research activities of DC superconducting power transmission lone in Chubu University,” 8th European Conference on Applied Superconductivity (EUCAS 2007) Journal of Physics: Conference Series 97, 2008, 012290] Some research groups have begun to analyze the design of high current cables using second-generation high temperature superconductor (HTS) tapes for transmission and distribution applications. It has been recognized that DC power distribution may play an important role in smaller scale power systems by either increasing system efficiency, increasing system reliability and robustness, or adding system flexibility, or some combination of all of these advantages. For example, a near-term commercial application of HTS cables for DC power distribution might be feasible for data server centers. Electric power consumption in modern data server centers often exceeds 10 MW per installation and is on a continuous growth path, representing a few percent of today's electricity consumption in the United States. Although most data centers are powered with AC systems, it is projected that DC systems can be more effective by reducing distribution losses and by being less expensive to install and operate. Several potential new applications for HTS DC cables could be for power distribution in microgrids and for transmission of electric power to the grid from alternative energy sources such as wind farms, solar farms, geothermal sites, fuel cells, etc.
It is therefore an object of the present invention to provide a high temperature superconductor cable that can be used in both AC and DC applications with particular applicability to DC applications requiring voltage over a wide range depending on application for example from relatively low voltage in the 400-600 V range for power distribution systems and up to 100 kV for transmission applications. It is also envisaged that HTS DC cables will carry significantly higher current than HTS AC cables with currents in the 10,000-25,000 A range, but not limited to these values. A further object is a power distribution cable that minimizes the cryogenic losses both in the leads and in a cryostat by using compact cable cross-sections.
Yet a further object of the invention is the development of superconductor cables for eventual implementation in large-scale DC power transmission systems as well as high current conductors for various electromagnetic equipment.